In the literature until today there are described in the literature two processes according to which 3-mercapto-propanediol-1,2, also called monothioglycerine, can be produced by the addition of hydrogen sulfide to glycidol.
According to L. Smith and B. Sjoberg (Ber. deutsch. chem. Ges. Vol. 69, pages 678-680, (1936)) and Sjoberg (Ber. deutsch. chem. Ges. Vol. 75, pages 13-29, (1942)) 1/3 mole of glycidol is dropped into a solution of 1/3 mole barium hydrogen sulfide saturated with hydrogen sulfide with running introduction of hydrogen sulfide. In the highest case the yield according to this process is 61% of theory, whereby it is stated that in increasing the charge beyond 1/3 mole the yield drops off. Besides there are formed higher molecular weight condensation products of glycidol. By distillation monothioglycerine can be separated from water and the byproducts. Because of the difficulties in enlarging the charge this method of production does not represent an industrially usable process for making monothioglycerine.
In German Pat. No. 910296 there is described a continuous process for the production of monothioglycerine whereby there should be produced yields of about 80-95%. Hereby there is employed a recycling apparatus which is charged with aqueous alcohol, e.g. isopropanol, and catalytic amounts, e.g. 0.3% of alkali or alkaline earth hydrogen sulfide, such as calcium hydrogen sulfide. Gaseous hydrogen sulfide is introduced into the apparatus in such manner that continuously hydrogen sulfide is present in the form of finely divided gas bubbles in the entire apparatus or solution and its concentration is greatest at the place of introduction of the glycidol. The temperature of the reaction mixture is held between 20.degree. and 35.degree. C. The reaction mixture is continuously drawn off from the recirculating apparatus.
By introduction of carbon dioxide the catalyst is precipitated as carbonate, the solution subsequently filtered and the alcohol employed recovered by distillation.
The water is removed in a next distillation step and the residue finally subjected to fractionation in vacuum whereby then monothioglycerine is obtained. In all of the examples the catalyst is removed before the distillation of the product from the crude product in order that the distillation of the product should proceed without difficulties.
In the first place the known process is tied to a special apparatus since there must be continuously present sufficient hydrogen sulfide to catch the hydroxide formed from the hydrogen sulfide. Otherwise, condensation reactions occur between glycidol and the monothioglycerine formed.
Besides the catalyst employed after the end of the reaction must be converted into a carbonate by introduction of carbon dioxide. The carbonate cannot be inserted again as such.
Furthermore, the distillation of the crude product can not be carried out in the presence the catalyst carbonate.
Therefore, the object of the invention is the development of a process which is industrially simple to carry out which likewise leads to high yields.